1. Field of the Invention
The present invention relates to an image processing apparatus, an image processing method, and a computer program product.
2. Description of the Related Art
Generally, in MFPs (Multi Function Peripherals) and printers, the printing cost of full-color output is higher than that of monochrome output. Accordingly, under some circumstances in which reduction of the printing cost is important, the use of the MFPs or printers may be supervised to be restricted to monochrome output by a supervisor of a system including the MFPs, the printers, and the like in many cases.
Even when the use of the MFP or the printer is restricted to the monochrome output, there may be circumstances in which a color output that uses a color (or colors) locally is desired for a document for in-house distribution of a company (for example, a document for in-house distribution with an annotation that is desired to be in red). In Japanese Patent No. 3560640, for the purpose of increasing the representational power of an output material that is output by an MFP, a printer, or the like, while suppressing the increase in printing cost, it is disclosed that two-color printing technology termed two-color copy or two-color printing is used. According to the two-color printing technology, a chromatic color is disposed in the middle of an achromatic color in a pin-point manner. It is highly effective in enabling the point that must be focused to be visually distinguished. Such an output may have merits over a simple full-color output depending on the design.
However, in the general two-color printing technology using an achromatic color and a chromatic color, it is only considered that the output material is represented by using two colors including an achromatic color and one chromatic color, but the relation between the two colors representing the output material such as color contrast (color difference) of the two colors is not considered. More specifically, in connection with the general two-color printing technology, in the case of using black and red for the two-color printing, what kind of attribute of the black fits the red most is not considered; but the output material is just represented with black that is just the color of a black coloring material used for generating an image. However, actually, due to the influence of a printing process, an image generating process, or the like, the color tone (a combination of brightness and saturation) of black that is output is deviated from an ideal state. Thus, depending on the manner in which the color tone of black is deviated and on the combination of black and a chromatic color, the color contrast between the chromatic color and the achromatic color might decrease; which results in a problem in that the representational power of the output material through two-color printing becomes weak. FIG. 22 is a diagram illustrating an example of a difference in color between the achromatic color and the chromatic color in the case in which an ideal black coloring material is used; and an example of a difference in chromaticity between the achromatic color and the chromatic color in the case in which a black coloring material that has been used practically is used. In the examples shown in FIG. 22, since the color tone of the black coloring material, which is practically used, is deviated from the ideal state (a state in which the saturation of the coloring material of the achromatic color is “zero”) in the same direction as the chromatic color due to saturation, the color contrast between the chromatic color and the achromatic color decreases.